When a vehicular motor to be mounted on a vehicle, such as a plug-in hybrid electric vehicle (PHEV) or an electric vehicle (EV) is controlled, it is necessary to satisfy a functional safety standard of ISO 26262 Therefore, achieving the following safety goal is typically required.
(1) The motor does not rotate in a direction reverse to an intentional rotating direction (ASIL-C or D).
(2) The motor does not output unintentional torque and a rotational speed (ASIL-C or D).
In order to achieve the above safety goal, it is necessary to dispose a safety mechanism that stops drive of the motor when abnormal rotation of the vehicular motor is detected.
Ina conventional resolver circuit, based on output signals (SIN signal and COS signal) from a resolver, a resolver digital converter (RDC) calculates and outputs a rotational angle θ of a motor to an external microcomputer. The external microcomputer performs feedback control to the motor based on the rotational angle θ of the motor supplied from the RDC.
Therefore, in order to dispose the above safety mechanism, the resolver circuit that calculates the rotational angle θ of the vehicular motor is required to be sound.
Regarding this point, based on an interval between zero crossing points of an excitation signal to be supplied to an excitation coil of the resolver, it has been known a device that samples the output signals (SIN signal and COS signal) from the resolver and calculates sin θ and cos θ so as to detect an abnormality in the resolver circuit (for example, refer to Patent Literature 1).